This invention relates to a process for oil agglomeration beneficiation of ground coal using a heavy oil or bitumen as an agglomerating vehicle and to a coal/heavy oil coprocessing in which the agglomerated coal forms part of the feedstock.
In many industrial applications of coal, e.g. fluidized or pulverized coal combustion, gasification, liquefaction, pyrolysis, coal-liquid mixtures, etc., fine grinding of coal is required. The ground coal mixture contains carbonaceous solids and inorganic solids and it is desirable to be able to separate the carbonaceous solids from the inorganic solids.
Also in coal mining processes the finely divided carbonaceous solids are produced as by-product and unless a suitable method is available for the use of such materials as fuel or the like, the finely divided carbonaceous solids constitute a waste.
The finely divided carbonaceous solids may be produced in dry form, or they may be in the form of aqueous slurries. For example, in coal mining operations, finely divided coal is produced as a by-product which is normally not completely recovered in coal cleaning operations.
In order to utilize finely ground coal as a feedstock for processes such as coal/oil coprocessing, there has been a need for improved methods of agglomerating the ground carbonaceous solids. It has long been known that mixing oils with aqueous slurries containing finely divided carbonaceous solids and finely divided inorganic solids results in selective agglomeration of carbonaceous solids. Many variations of these processes are known and two examples are those shown in Capes, et al. U.S. Pat. No 3,365,066 and Puddington, et al. U.S. Pat. No. 3,268,071.
It is known that the selective wetting of carbonaceous solids by oil and formation of the agglomerate in an aqueous slurry containing finely divided carbonaceous solids and inorganic solids is based on the difference between surface properties of the carbonaceous solids and inorganic solids. While carbonaceous solids are usually hydrophobic and oleophilic, the inorganic solids are hydrophilic. It has been found that cleaning of low rank coals such as sub-bituminous, lignites and the like as well as oxidized (weathered) higher rank bituminous coals do not result in the production of agglomerates of finely divided carbonaceous solids and oil when mixed with quantities of oil sufficient to agglomerate the carbonaceous solids contained in aqueous slurries mostly due to the lower hydrophobicity as compared to non-oxidized higher rank bituminous coals. Decrease in rank from bituminous to sub-bituminous and further to lignite is usually associated with gradually less hydrophobic balance of the coal surface properties. It is known that low rank or oxidized coal can be agglomerated with oil if a concentrated electrolyte such as concentrated sulphuric acid, concentrated hydrochloric acid or sulphur trioxide gas is mixed with the aqueous slurry.
It is an object of the present invention to provide an improved technique for producing coal/oil agglomerates which may be used in coal/oil coprocessing.